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•A phragmites communis like microstructure was constructed successfully.•Interconnected CFs network acts as thermal transfer path in PDMS composite.•The vertical CF/PDMS composite ...exhibits excellent heat dissipation performance.
The high integration and high power devices cause serious local heat accumulation, which will damage the reliability and service life of devices. Efficient heat dissipation has become priority issues for electronic devices. As a one-dimension thermal conductive fillers, carbon fibers (CFs) exhibits ultra-high thermal conductive performance. However, the superiority is not fully utilized by traditional approaches especially for short CFs. In this work, a micro-phragmites communis structure was constructed for enhance thermal transfer property of composites. And the composites were obtained by immersed in polydimethylsiloxane (PDMS) with vacuum-assisted. Owing to vertical CFs structure, the through-plane thermal conductivity of polymer composites achieving 6.04 W m−1 K−1 at low CFs loading. Further, the surface temperature variation of composites in heating and cooling process was observed by infrared camera, and it exhibits excellent heat transfer performance. The applicability of the high thermal conductive composite was investigated by applied in CPU heat dissipation. This work reveals promising approaches for fully utilize the ultra-high axes thermal conductivity of CFs to prepared high thermal conductive composites.
Urged by the increasing power and packing densities of integrated circuits and electronic devices, efficient dissipation of excess heat from hot spot to heat sink through thermal interface materials ...(TIMs) is a growing demand to maintain system reliability and performance. In recent years, graphene‐based TIMs received considerable interest due to the ultrahigh intrinsic thermal conductivity of graphene. However, the cooling efficiency of such TIMs is still limited by some technical difficulties, such as production‐induced defects of graphene, poor alignment of graphene in the matrix, and strong phonon scattering at graphene/graphene or graphene/matrix interfaces. In this study, a 120 µm‐thick freestanding film composed of vertically aligned, covalently bonded graphene nanowalls (GNWs) is grown by mesoplasma chemical vapor deposition. After filling GNWs with silicone, the fabricated adhesive TIMs exhibit a high through‐plane thermal conductivity of 20.4 W m−1 K−1 at a low graphene loading of 5.6 wt%. In the TIM performance test, the cooling efficiency of GNW‐based TIMs is ≈1.5 times higher than that of state‐of‐the‐art commercial TIMs. The TIMs achieve the desired balance between high through‐plane thermal conductivity and small bond line thickness, providing superior cooling performance for suppressing the degradation of luminous properties of high‐power light‐emitting diode chips.
Graphene nanowalls, composed of high‐quality, vertically aligned, and covalently bonded graphene frameworks, exhibit excellent ability to improve the thermal conductivity of polymer‐based thermal interface materials. The resulting composites show a through‐plane thermal conductivity of 20.4 W m−1 K−1 at a filler content of 5.6 wt%, resulting in ≈1.5 times higher cooling efficiency compared to that of a commercial thermal pad.
In this study, we report a facile approach to fabricate epoxy composite incorporated with silicon carbide nanowires (SiC NWs). The thermal conductivity of epoxy/SiC NWs composites was thoroughly ...investigated. The thermal conductivity of epoxy/SiC NWs composites with 3.0 wt% filler reached 0.449 Wm
K
, approximately a 106% enhancement as compared to neat epoxy. In contrast, the same mass fraction of silicon carbide micron particles (SiC MPs) incorporated into epoxy matrix showed less improvement on thermal conduction properties. This is attributed to the formation of effective heat conduction pathways among SiC NWs as well as a strong interaction between the nanowires and epoxy matrix. In addition, the thermal properties of epoxy/SiC NWs composites were also improved. These results demonstrate that we developed a novel approach to enhance the thermal conductivity of the polymer composites which meet the requirement for the rapid development of the electronic devices.
The self-attraction of nanowires (NWs) would lead to NWs bunching up together when fabricated in high density and the short circuit of NW-based devices during service. However, the underlying ...mechanism of the self-attraction of NWs remains debatable due to the lack of
in situ
characterization of the attraction. In this study, a versatile method of
in situ
investigating the self-attraction of NWs was developed. The attractive force between two NWs and their distance can be determined quantitatively in the process of attraction under an optical microscope, eliminating the influence of electron beam in electron microscopes. With this approach, the self-attraction of SiC NWs was investigated and a two-stage mechanism for the self-attraction was proposed. The electrostatic force between two individual SiC NWs increased as their distance decreased, and acted as the initial driving force for the attraction of NWs. SiC NWs remained in contact under van der Waals force until they separated when external force exceeded van der Waals force. The charge density and the Hamaker constant of SiC NWs were determined to be 1.9 × 10
−4
C·m
−2
and 1.56 × 10
−19
J, which played an important role in the attraction of NWs. The results shed light on the mechanism of self-attraction among NWs and provide new insights into fabricating high-quality NWs and developing high-performance NW-based devices.
We investigated the effects of texture shape and machining conditions on the magnitude of the texture effect of a textured diamond cutting tool in order to optimize its shape. The texture was ...fabricated on the surface of a diamond cutting tool by utilizing a focused ion beam and subsequent heat treatment method. Machining experiments with an aluminum alloy and nickel phosphorus (NiP) were carried out to investigate the effect of the texture shape on the machining performance. The magnitude of the texture effect changed by the machining parameters such as the cutting speed and species of work materials. These parameters affect the contact length between the tool and work materials, and the relation between the contact length and the shape of the texture is a dominant factor when determining the magnitude of the texture effect. In particular, the position of the first groove is very important in low-speed cutting. Large decreases in the cutting force and friction coefficient were obtained even for NiP. The machined surface quality was also improved by the texturing of NiP. These results indicate the effectiveness of a textured diamond cutting tool and were effective in the optimization of the texture shape.
•The effects of texture shape and machining conditions on texture effect was evaluated.•Large decreases in the cutting force and friction coefficient were obtained for NiP.•The machined surface was improved by the texturing of NiP at low speed cutting.
Diamond-like carbon (DLC) coatings are effective in protecting the key components of marine equipment and can greatly improve their short-term performance (1.5~4.5 h). However, the lack of ...investigation into their long-term (more than 200 h) performance cannot meet the service life requirements of marine equipment. Here, three multilayered DLC coatings, namely Ti/DLC, TiC
/DLC, and Ti-TiC
/DLC, were prepared, and their long-term corrosion resistance was investigated. Results showed that the corrosion current density of all DLC coatings was reduced by 1-2 orders of magnitude compared with bare 316L stainless steel (316Lss). Moreover, under long-term (63 days) immersion in a 3.5 wt.% NaCl solution, all DLC coatings could provide excellent long-term corrosion protection for 316Lss, and Ti-TiC
/DLC depicted the best corrosion resistance; the polarization resistances remained at ~3.0 × 10
Ω·cm
after immersion for 63 days, with more interfaces to hinder the penetration of the corrosive media. Meanwhile, during neutral salt spray (3000 h), the corrosion resistance of Ti/DLC and TiC
/DLC coatings showed a certain degree of improvement because the insoluble corrosion products at the defects blocked the subsequent corrosion. This study can provide a route to designing amorphous carbon protective coatings for long-term marine applications in different environments.
Bulk diamonds show great potential for optical applications such as for use in infrared (IR) windows and temperature sensors. The development of optical-grade bulk diamond synthesis techniques has ...facilitated its extreme applications. Here, two kinds of bulk single-crystal diamonds, a high-pressure and high-temperature (HPHT) diamond and a chemical vapor deposition (CVD) diamond, were evaluated by Raman spectroscopy and Fourier Transform Infra-Red (FTIR) spectroscopy at a range of temperatures from 80 to 1200 K. The results showed that there was no obvious difference between the HPHT diamond and the CVD diamond in terms of XRD and Raman spectroscopy at 300–1200 K. The measured nitrogen content was ~270 and ~0.89 ppm for the HPHT diamond and the CVD diamond, respectively. The moderate nitrogen impurities did not significantly affect the temperature dependence of Raman spectra for temperature-sensing applications. However, the nitrogen impurities greatly influence FTIR spectroscopy and optical transmittance. The CVD diamond showed higher transmittance, up to 71% with only a ~6% drop at temperatures as high as 873 K. This study shows that CVD bulk diamonds can be used for IR windows under harsh environments.
Highlights
A three-tiered thermal interface materials was proposed with the through-plane thermal conductivity up to176 W m
−1
K
−1
and contact thermal resistance as low as 4–6 K mm
2
W
−1
(double ...sides).
The liquid metal acts as a buffer layer to connect vertically aligned graphene with the rough heater/heat sink, improving effective contact thermal conductance by more than an order of magnitude.
Developing advanced thermal interface materials (TIMs) to bridge heat-generating chip and heat sink for constructing an efficient heat transfer interface is the key technology to solve the thermal management issue of high-power semiconductor devices. Based on the ultra-high basal-plane thermal conductivity, graphene is an ideal candidate for preparing high-performance TIMs, preferably to form a vertically aligned structure so that the basal-plane of graphene is consistent with the heat transfer direction of TIM. However, the actual interfacial heat transfer efficiency of currently reported vertically aligned graphene TIMs is far from satisfactory. In addition to the fact that the thermal conductivity of the vertically aligned TIMs can be further improved, another critical factor is the limited actual contact area leading to relatively high contact thermal resistance (20–30 K mm
2
W
−1
) of the “solid–solid” mating interface formed by the vertical graphene and the rough chip/heat sink. To solve this common problem faced by vertically aligned graphene, in this work, we combined mechanical orientation and surface modification strategy to construct a three-tiered TIM composed of mainly vertically aligned graphene in the middle and micrometer-thick liquid metal as a cap layer on upper and lower surfaces. Based on rational graphene orientation regulation in the middle tier, the resultant graphene-based TIM exhibited an ultra-high thermal conductivity of 176 W m
−1
K
−1
. Additionally, we demonstrated that the liquid metal cap layer in contact with the chip/heat sink forms a “liquid–solid” mating interface, significantly increasing the effective heat transfer area and giving a low contact thermal conductivity of 4–6 K mm
2
W
−1
under packaging conditions. This finding provides valuable guidance for the design of high-performance TIMs based on two-dimensional materials and improves the possibility of their practical application in electronic thermal management.
In the present study, the tribological properties of diverse crystalline diamond coating with micro (MCD) and nanometer (NCD) sizes, fabricated by the microwave plasma chemical vapor deposition ...(MPCVD) method, are systematically investigated in dry and seawater environments, respectively. Owing to the SiO2 lubricating film with extraordinary hydrophilicity performance by a tribochemical reaction, the average friction coefficient (COF) and wear rate of NCD coating under seawater decreased by 37.8% and 26.5%, respectively, comparing with in dry conditions. Furthermore, graphite would be generated with the increment of surface roughness. Graphite transformed from the diamond under high contact pressure. Thus, with the synergism between SiO2 lubricating film with extraordinary hydrophilicity performance and graphite, the corresponding COF and wear rate of MCD would be further decreased by up to 64.1% and 39.5%. Meanwhile, various characterizations on morphology, spectra, and tribological performance of the deposited diamond coating were conducted to explore the in-depth mechanism of the enhanced tribological performance of our NCD and MCD coatings in the extreme under seawater working conditions. We envision this work would provide significant insights into the wear behavior of diamond coatings in seawater and broaden their applications in protective coatings for marine science.
Amorphous carbon coatings by various physical vapor deposition (PVD) have been widely attempted for enhancing both anti-wear and corrosion resistance of bulk materials used in harsh marine ...environments. However, PVD coatings are apt to be worn due to the existence of growth defects mostly like macro-size nodular particles. In this work, we deliberately fabricated the SiO2 nanoparticles with a size of 200 nm as nodular defects in Cr and graphite-like carbon (Cr/GLC) multilayer coatings, and the dependence of tribocorrosion behavior of coating on the nodular defects was focused by the comprehensively tribological and electrochemical tests. The results showed that introducing SiO2 nodular particles could not degrade the mechanical properties of Cr/GLC coating, but significantly accelerated both the abrasive wear in early sliding-stage under dry friction and the corrosive failure in chloride solution. Particularly, once the tribocorrosion tests in 3.5 wt.% NaCl solution were conducted for the Cr/GLC coating with nodular defects, the distinct ploughing damage originated from abrasive wear promoted the localized spallation of coatings, which thereafter enabled the easy water wedging along spallation for the substantial catastrophe of coatings. The present observations could evident the importance to fabricate the defect-free protective coatings required for harsh tribocorrosion applications.
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